The field of the invention is automotive electric connectors.
Spark plug boots are typically tubular elastomeric silicone members enclosing a portion of a spark plug and a potion of an ignition cable and frequently have a straight or generally L-shaped configuration. Despite their widespread use in many automobiles, problems with respect to thermal stability of the boots persist due to thermal degradation of the elastomeric silicone in the engine compartment, a problem that may especially be compounded by gasoline vapors and exhaust fumes. Where spark plug boots are thermally damaged, the boots are typically replaced which may incur significant costs, particularly where the boot is permanently coupled to the ignition cable. In order to reduce the frequency of replacing spark plug boots, various heat shields have been developed to protect the boot at least partially from thermal radiation.
For example, DeBolt teaches in U.S. Pat. No. 4,671,586 a spark plug shield and boot seal assembly in which a heat shield is rotationally interlocked with a boot seal assembly. DeBolt""s heat shield further provides internal air flow passages and can advantageously be utilized as a boot seal removal tool for service. Although DeBolt""s heat shield may facilitate installation and may improve the overall life span of a spark plug boot, some problems with DeBolt""s heat shield remain. For example, by providing internal air flow passages, the temperature in the boot proximal to the internal air flow passages may disadvantageously increase due to thermal convection within the passages. Moreover, thermal conduction along the heat shield may increase the temperature in areas of the heat shield that are not directly exposed to a heat source, thereby potentially reducing the thermal protection.
In another example, U.S. Pat. No. 5,348,486 to Tura and Germ, a thin metallic heat shield is stamped from a sheet metal and wrapped around the boot to form a heat shield. Tura""s heat shield engages with the hex of the metal shell of the spark plug via a pair of ears that protrude from the heat shield. Forming a heat shield from a sheet metal generally allows relatively simple fabrication and may potentially reduce costs. However, problems similar to the problems of DeBolt""s heat shield remain. Most importantly, Tura""s heat shield merely provides a passive deflector that deflects heat radiation, but tends to fails to provide insulation from heat convection and thermal conduction within the heat shield. Still further, both Tura ""s and DeBolt""s heat shields are generally inflexible, thereby eliminating the advantage of having a somewhat flexible spark plug boot.
Although various heat shields for spark plug boot assemblies are known in the art, all or almost all of them fail to provide protection from heat convection and thermal conduction within the heat shield. Therefore, there is still a need to provide spark plug boot assemblies with improved heat shields.
The present invention is directed to a spark plug boot assembly in which a heat barrier surrounds a boot having ends for receiving an ignition cable and a spark plug, respectively. The heat barrier has an outer wall and an inner wall that are coupled together to define a cavity, with a thermal insulator disposed in the cavity. The inner wall of the heat barrier snugly engages with the outer surface of the boot, and may further comprise a silicon coating that faces the outer surface of the boot.
In one aspect of the inventive subject matter, the thermal insulator may comprise ceramic wool, microporous amorphous silica, fiberglass, or polymeric foam. While it is generally contemplated that the outer and inner walls are fabricated from metal, it is preferred that the metal is stainless steel foil having a thickness of about 0.002-0.005 inch and it is even more preferred that the outer wall is corrugated.
In another aspect of the inventive subject matter, both the boot and the heat barrier can be L-shaped, and it is particularly preferred that the heat barrier is electrically coupled to a metal portion of a spark plug to electrically ground the heat barrier.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawing.